Why is this? I am trying to reduce the size of the google + button and I compared both. Why is the one on the dev tools different from the custom.css?
don't change the subtheme .css
in general - css and js can be minified.
also css can be created from the less file that is not user-friendly.
just add info to custom.css
you will be alot happier.
and use cssedit if you have cloudflare and caching.
in answer to your question about the NOT custom.css file - its just processed to save on size.
and re-read the description here:
read some tutorial on css inheritance css specificity and less
just override in custom.css
make the rule more specific or use !important.
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.